Zeolite HY and Silica Gel as New and Efficient Heterogenous Catalysts for the Synthesis of Triarylimidazoles under Microwave Irradiation

Synthesis of imidazole derivatives from β-lapachone and related compounds using microwave and supported reagents

“…The low yields for 3 and 4 are in accordance with literature data, where acidic conditions afforded better results. [11][12][13]17 In addition, it was also investigated whether these reactions could occur efficiently without a support or microwave energy (other conditions kept equal). The experiments were carried out for the synthesis of compound 2a.…”

“…17 The availability of microwave technology for synthetic purposes has allowed the efficient preparation of 2,4,5-trissubstituted and 1,2,4,5-tetrassubstituted imidazoles. Further observed benefits, that were occasionally associated with solid supports such as silica, alumina, clays, amongst others, [11][12][13] included improved yields, and dramatic reductions in reaction time and quantities of solvent used (AcOH). 14,15 Interestingly, the best supports found in these studies were always the acidic in nature.…”

“…8,9 These imidazole derivatives were prepared by conventional methods. 9 As part of an ongoing study into the use of microwave activation and the use of supported reagents, in this case ammonium acetate, we investigated the preparation of the previously unknown simple imidazole derivatives of β-lapachone and related ortho-quinones with formaldehyde.Microwave activation has provided significant improvement on heterocyclic synthesis, 10 including imidazoles, with [11][12][13] or without support, 14,15 with reduction/ elimination of solvents, decreased reaction times and equal or improved yields. …”

“…Microwave activation has provided significant improvement on heterocyclic synthesis, 10 including imidazoles, with [11][12][13] or without support, 14,15 with reduction/ elimination of solvents, decreased reaction times and equal or improved yields.…”

A convenient synthesis of 2,4,5-triarylimidazoles catalyzed by Y(TFA)3

“…Later, the procedure of three components condensation of benzil, benzaldehyde derivatives, and ammonium acetate was frequently employed. In this procedure, [HeMIM]BF 4 (6), Eu(OTf) 3 (7), Keggintype heteropolyacid (8), HClO 4 ÁSiO 2 (9), iodine (10), zeolite HY and silica gel (11), silica sulfuric acid (12), NiCl 2 ×6H 2 O (13), and Yb(OTf) 3 (14) were used as catalysts to synthesize triarylimidazoles. Moreover, the synthesis of these triarylimidazoles has been usually carried out in the presence of microwave irradiation (15Á18).…”